A honeycomb structure has been used in a filter for trapping particulate in exhaust gas of an internal combustion engine, boiler, and the like, particularly diesel particulate.
In general, as shown in FIGS. 9(a) and (b), the honeycomb structure for use in this purpose has a large number of cells 3 which are partitioned from one another by partition walls 2 and which extending through an X-axis direction, and has a structure in which the cells 3 adjacent to each other are plugged in one end on an opposite side so that end faces have checkered patterns. In such a honeycomb structure, a fluid to be treated flows in the cell 3 not plugged at inflow end face 42, that is, plugged at outflow end face 44, passes through the porous cell walls 2, and is discharged via the adjacent cells 3, that is, the cell 3 plugged at the inflow end face 42 and not plugged at outflow end face 44. In this case, the cell walls 2 act as a filter. For example, soot discharged from a diesel engine is trapped by the cell walls and deposited on the cell walls. In the honeycomb structure used for such way, the rapid temperature change of exhaust gas and the local heating makes non-uniform the temperature distribution inside the honeycomb structure, and there have been problems such as crack generation by thermal stress in honeycomb structure and the like. When the honeycomb structure is used particularly as a filter for trapping a particulate substance in an exhaust gas emitted from a diesel engine (it is hereinafter referred to as DPF), it is necessary to burn the fine carbon particles deposited on the filter to remove the particles and regenerate the filter and, in that case, high temperatures are inevitably generated locally in the filter; as a result, by nonuniformity of regeneration temperature, a large thermal stress and cracks have tended to generate.
To solve the problem, a method of bonding a plurality of divided segments of the honeycomb structure by a bond material has been proposed. For example, in U.S. Pat. No. 4,335,783, a method for manufacturing a honeycomb structure is disclosed in which a large number of honeycomb members are bonded by discontinuous bond materials. Also in JP-B-61-51240 is proposed a thermal-shock resistant rotary regenerating thermal exchanging method which comprises forming, by extrusion, matrix segments of honeycomb structure made of a ceramic material, firing them, making smooth, by processing, the outer peripheral portions of the fired segments, coating the to-be-bonded areas of the resulting segments with a ceramic adhesive having, when fired, substantially the same chemical composition as the matrix segments and showing a difference in thermal expansion coefficient, of 0.1% or less at 800° C., and firing the coated segments. In SAE document 860008 of 1986, a ceramic honeycomb structure is disclosed in which the honeycomb segment of cordierite is similarly bonded with cordierite cement. Further in JP-A-8-28246 is disclosed a ceramic honeycomb structure obtained by bonding honeycomb ceramic members with an elastic sealant made of at least a three-dimensionally intertwined inorganic fiber, an inorganic binder, an organic binder and inorganic particles. Attempts have also been made to prepare the honeycomb structure using silicon carbide based materials high in thermal conductivity and heat resistance so that a local high temperature is prevented and the honeycomb structure is prevented from being broken by the thermal stress.
By this segmenting, and/or by the use of the materials high in heat resistance, such as the silicon carbide based material, the cracks by the thermal stress can be reduced to some degree. However, when the resistance to the thermal stress of the segment itself can further be enhanced, cost can be reduced by decrease of the number of segments, and regeneration efficiency can also be enhanced.